Foamed polymer and process for production thereof

ABSTRACT

A foamed isocyanate-based polymer having a cellular structure and comprising a non-surface cross-linked superabsorbent polymer, the foamed polymer being capable of: (i) absorbing at least about 10 times its weight of a 0.9 wt./wt. % aqueous NaCl solution maintained at a temperature of from about 20° to about 25° C., and (ii) retaining at least about 10 times its weight of absorbed aqueous NaCl solution which is bound to the superabsorbent polymer. A process for producing the foamed isocyanate-based polymer is also described. The process comprises the steps of: contacting an isocyanate, an active hydrogen-containing compound, an aqueous blowing agent, a catalyst and a non-surface cross-linked superabsorbent polymer, the superabsorbent polymer being capable of absorbing at least about 10 times its weight of a 0.9 wt./wt. % aqueous NaCl solution maintained at a temperature in the range of from about 20° to about 25° C.; and expanding the reaction mixture to produce the foamed isocyanate-based polymer. The active hydrogen-containing compound comprises from about 10% to 100% by weight of a hydrophilic active hydrogen-containing compound and from 0 to about 90% by weight a non-hydrophilic active hydrogen-containing compound. The foamed isocyanate-based polymer is ideally suitable for use in an absorption layer in a personal hygiene device.

This application is a division of application Ser. No. 08/674,242 filedJul. 1, 1996 now U.S. Pat. No. 5,624,971.

DESCRIPTION OF THE PRIOR ART

Isocyanate-based polymers are known in the art. Generally, those ofskill in the art understand isocyanate-based polymers to bepolyurethanes, polyureas, polyisocyanurates and mixtures thereof.

It is also known in the art to produce foamed isocyanate-based polymers.Indeed, one of the advantages of isocyanate-based polymers compared toother polymer systems is that the chemistry can be used to achievedesired product properties in situ.

One of the conventional ways to produce a polyurethane foam is known asthe "one-shot" technique. In this technique, the isocyanate, a suitablepolyol, a catalyst, water (which acts to generate carbon dioxide as theblowing agent and can optionally be supplemented with one or moresecondary organic blowing agents) and other additives are mixed togetherat once using, for example, a mechanical or impingement mixer.Generally, if one were to produce a polyurea, the polyol would bereplaced with a suitable polyamine. A polyisocyanurate may result fromcyclotrimerization of the isocyanate component. Urethane-modifiedpolyureas or polyisocyanurates are known in the art. In either scenario,the reactants would be intimately mixed quickly using a suitable mixer.

Another technique for producing foamed isocyanate-based polymers isknown as the "prepolymer" technique. In this technique, a prepolymer ofpolyol and isocyanate (in the case of a polyurethane) are reacted in aninert atmosphere to form a liquid polymer terminated with isocyanategroups. To produce the foamed polymer, the prepolymer is thoroughlymixed with water and, optionally, a polyol (in the case of producing apolyurethane) or a polyamine (in the case of producing a polyurea) inthe presence of a catalyst or a cross-linker.

As is known by those of skill in the art, many conventionalisocyanate-based foams are non-hydrophilic (i.e. relativelyhydrophobic). Such foams generally have an aversion to aqueous fluids.Practically, this results in such foams being unable to absorb or pickup significant quantities of aqueous fluids (e.g. the foams will floaton water) other than by mechanical entrainment. Accordingly, such foamsare vitally never used in an application in which significant aqueousfluid absorption and retention is a desired feature.

In copending U.S. patent application Ser. No. 08/413,433 (Wilson) and08/554,896 (Wilson), the contents of each of which are herebyincorporated by reference, there is disclosed a foamed isocyanate-basedpolymer having a cellular structure and containing a superabsorbentmaterial, the polymer being capable of: (i) absorbing at least about 20times its weight of an aqueous fluid maintained at a temperature of fromabout 20° to about 25° C., and (ii) retaining at least about 20 timesits weight of absorbed aqueous fluid which is bound to thesuperabsorbent material. The foamed isocyanate-based polymer disclosedin the Wilson '433 and '896 applications may be produced by a processwhich comprises reacting and expanding (via a suitable catalyst andblowing agent) a mixture comprising an isocyanate, an activehydrogen-containing compound and a superabsorbent material. Thesuperabsorbent material is capable of absorbing at least about 20 timesits weight of an aqueous fluid maintained at a temperature in the rangeof from about 20° to about 25° C. The active hydrogen-containingcompound comprises from about 10% to 100% by weight of a hydrophilicactive hydrogen-containing compound and from 0 to about 90% by weight anon-hydrophilic active hydrogen-containing compound. The foamedisocyanate-based polymer is ideally suitable for use in an absorptionlayer in a personal hygiene device.

An example of known superabsorbent materials are superabsorbentpolymers. A good discussion on superabsorbent polymers may be found in"SUPERABSORBENT POLYMERS Science and Technology", ACS Symposium Series573, Edited by Bucholz et al. (1994), the contents of which are herebyincorporated by reference.

A superabsorbent material, such as a superabsorbent polymer, may bethought of as an ionic hydrocolloid. Generally, such a material isconsidered to be superabsorbent if it is able to imbibe, absorb or gelat least about 10 times its weight of a fluid and retain the fluid undermoderate pressure (this property is also known as Absorbency Under Loador AUL, and is discussed in more detail hereinbelow), for example usingthe protocol discussed U.S. Pat. No. 5,147,343, the contents of whichare hereby incorporated by reference.

Current conventional, commercial superabsorbent polymers arecross-linked polymers of partially neutralized acrylic acid--see Chapter2 of "SUPERABSORBENT POLYMERS Science and Technology", ACS SymposiumSeries 573, Edited by Bucholz et al. (1994), the contents of which arehereby incorporated by reference. The cross-linked polymers are actuallyterpolymers of acrylic acid, sodium acrylate and a cross-linker. Suchpolymers may be produced by free-radical polymerization in aqueoussolution, graft copolymerization or suspension polymerization and,depending on the degree of cross-lining of the polymers, are referred toas first generation (lightly cross-linked) and second generation(cross-linked) superabsorbent polymers.

Once the cross-linked polymers are produced (these may be regarded as"non-surface cross-inked superabsorbent polymers"), it is known in theart to post-treat them to effect surface cross-linking (thesepost-treated materials may be regarded as "surface cross-inkedsuperabsorbent polymers"). This further cross-linking at the surface ofthe particles is known to alter the absorption rate of the polymer--seepublished British patent application 2,119,384 and U.S. Pat. No.4,497,930, the contents of each of which are hereby incorporated byreference.

Surface cross-inked superabsorbent polymers contain a discontinuousnetwork and thus, have offered a number of variations in productproperties. As discussed in Chapter 8 of "SUPERABSORBENT POLYMERSScience and Technology", ACS Symposium Series 573, Edited by Bucholz etal. (1994), the contents of which are hereby incorporated by reference,first and second generation (non-surface cross-linked) superabsorbentpolymers suffer from the fact that their retention capacity variesdirectly with the degree of cross-linking whereas their AUL variesindirectly with the degree of cross-linking--this is illustrated in FIG.1 which includes retention capacity and AUL for first and secondgeneration superabsorbent polymers. Third generation (surfacecross-linked) superabsorbent polymers were developed as an improvementover first and second generation superabsorbent polymers - this isillustrated in FIG. 2 which includes retention capacity and AUL forthird generation superabsorbent polymers. Thus, third generation(surface cross-linked) superabsorbent polymers are characterized by anincreased AUL compared to second generation (non-surface cross-linked)superabsorbent polymers. Not surprisingly, third generation (surfacecross-inked) superabsorbent polymers are significantly more costly (e.g.10% or more) than second generation (non-surface cross-linked)superabsorbent polymers. Thus, on an equivalent basis, improvedperformance is achieved at an increased cost.

While the foamed isocyanate-based polymer disclosed in the Wilson '433and '896 applications represents a significant advance in the art, thereis continuous need for improvements in the art. For example, there is acontinuous need to improve and optimize the fluid absorbing efficiencyof the superabsorbent material contained in the foam matrix. Dependingon the particular application for the foamed polymer, such animprovement would allow one or more of: (i) reduction of the amount ofsuperabsorbent material required to meet a specified fluidabsorption/retention (thereby reducing the cost of producing the foamedpolymer), (ii) the ability to improve the performance of the foamedpolymer (i.e. increasing the fluid absorption/retention thereof) beyondthat conventionally obtained, and (iii) reduction in the cost of productof the foamed polymer to meet a specific performance criterion.

In light of the above, it would be advantageous to have a foamedisocyanate-based polymer which is hydrophilic and characterized byimproved absorption (or pick up) and retention of an aqueous fluid. Itwould be further advantageous if such a foam could be produced in arelatively uncomplicated way and possessed reproducible physicalproperties.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel foamedisocyanate-based polymer having improved aqueous fluid absorption andretention properties.

It is an object of the present invention to provide a novel process forproducing such a foamed isocyanate-based polymer.

It is another object of the present invention to provide a novelpersonal hygiene device incorporating such a foamed isocyanate-basedpolymer.

Accordingly, in one of its aspects, the present invention provides afoamed isocyanate-based polymer having a cellular structure andcomprising a non-surface cross-linked superabsorbent polymer, the foamedisocyanate-based polymer being capable of: (i) absorbing at least about10 times its weight of a 0.9 wt./wt. % aqueous NaCl solution maintainedat a temperature of from about 20° to about 25° C., and (ii) retainingat least about 10 times its weight of absorbed aqueous NaCl solutionwhich is bound to the superabsorbent polymer.

In another of its aspects, the present invention provides a foamedpolyurethane polymer comprising non-surface cross-linked poly(acrylicacid alkali metal salt) in an amount in the range of from about 5 toabout 150 parts by weight per hundred parts by weight of polyol used toproduce the foamed polyurethane polymer, the polymer being capable of:(i) absorbing from about 10 to about 20 times its weight of a 0.9wt./wt. % aqueous NaCl solution maintained at a temperature of fromabout 20° to about 25° C., and (ii) retaining from about 10 to about 20times its weight of absorbed aqueous NaCl solution which is bound to thenon-surface cross-inked poly(acrylic acid alkali metal salt).

In yet another of its aspects, the present invention provides a processfor producing a foamed isocyanate-based polymer comprising the steps of:

providing a substantially uniform mixture comprising an isocyanate, anactive hydrogen-containing compound and a non-surface cross-inkedsuperabsorbent polymer, the non-surface cross-linked superabsorbentpolymer being capable of absorbing at least about 10 times its weight ofa 0.9 wt./wt. % aqueous NaCl solution maintained at a temperature in therange of from about 20° to about 25° C.;

adding to the substantially uniform mixture an aqueous blowing agent anda catalyst to form a reaction mixture; and

expanding the reaction mixture to produce the foamed isocyanate-basedpolymer;

wherein the active hydrogen-containing compound comprises from about 10%to 100% by weight of a hydrophilic active hydrogen-containing compoundand from 0 to about 90% by weight a non-hydrophilic activehydrogen-containing compound.

In an alternate embodiment of the present process, a process is providedfor producing a foamed isocyanate-based polymer comprising the steps of:

providing a substantially uniform mixture comprising an aqueous blowingagent, a catalyst, an active hydrogen-containing compound and anon-surface cross-linked superabsorbent polymer, the non-surfacecross-linked superabsorbent polymer being capable of absorbing at leastabout 10 times its weight of a 0.9 wt./wt. % NaCl solution maintained ata temperature in the range of from about 20° to about 25° C.;

adding to the substantially uniform mixture an isocyanate to form areaction mixture; and

expanding the reaction mixture to produce the foamed isocyanate-basedpolymer;

wherein the active hydrogen-containing compound comprises from about 10%to 100% by weight of a hydrophilic active hydrogen-containing compoundand from 0 to about 90% by weight a non-hydrophilic activehydrogen-containing compound.

In a further alternate embodiment of the present process, a process isprovided for producing a foamed isocyanate-based polymer comprising thesteps of:

providing a dispersion comprising a substantially uniform mixture of anactive hydrogen-containing compound and a non-surface cross-linkedsuperabsorbent polymer, the non-surface cross-linked superabsorbentpolymer being capable of absorbing at least about 10 times its weight ofa 0.9 wt./wt. % aqueous NaCl solution maintained at a temperature in therange of from about 20° to about 25° C.;

contacting the dispersion with an isocyanate, a catalyst and an aqueousblowing agent to form a reaction mixture; and

expanding the reaction mixture to produce the foamed isocyanate-basedpolymer;

wherein the active hydrogen-containing compound comprises from about 10%to 100% by weight of a hydrophilic active hydrogen-containing compoundand from 0 to about 90% by weight a non-hydrophilic activehydrogen-containing compound.

When any of the embodiments of the process are used to prepare a foamedpolyurethane or a foamed urea-modified polyurethane, it is possible, andindeed preferred, to use a single polyol or a mixture of polyols whichpossesses an overall ethylene oxide content in the range of from about15 to about 80, preferably from about 20 to about 70, more preferablyfrom about 35 to about 70, most preferably from about 50 to about 65,percent by weight, the remainder comprised of other polyoxyalkylenegroups such as propylene oxide, butylene oxide or mixtures thereof.

In yet another of its aspects, the present invention provides a personalhygiene device having a bodily fluid absorbent layer consistingessentially of a foamed isocyanate-based polymer having a cellularstructure and comprising a non-surface cross-linked superabsorbentpolymer, the foam isocyanate-based polymer being capable of: (i)absorbing at least about 10 times its weight of a 0.9 wt./wt. % aqueousNaCl solution maintained at a temperature of from about 20° to about 25°C., and (ii) retaining at least about 10 times its weight of absorbedNaCl solution which is bound to the non-surface cross-linkedsuperabsorbent polymer.

As used throughout this specification, the term "non-surfacecross-linked superabsorbent polymer" is intended to mean asuperabsorbent polymer which, after polymerization is not subjected toany further treatment to increase the cross-linking density on thesurface thereof. Thus, in the context of the present invention, thefirst and second superabsorbent polymers discussed hereinabove fallwithin the term "non-surface cross-linked superabsorbent polymer"whereas the third generation superabsorbent polymers discussedhereinabove are outside the scope of the term "non-surface cross-linkedsuperabsorbent polymer". Further, as used throughout this specification,the term "isocyanate-based polymer" is intended to mean, inter alia,polyurethane, polyurea and polyisocyanurate. Further, the terms "0.9wt./wt. % aqueous NaCl solution" and "saline solution" are usedinterchangeably through this specification and are intended to have thesame meaning.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described with reference tothe accompanying drawings, in which:

FIG. 1 is a graphical illustration of the retention capacity and AUL asa function of the degree of cross-linking for first and secondgeneration (non-surface cross-linked) superabsorbent polymers;

FIG. 2 is a graphical illustration of the retention capacity and AUL asa function of the degree of cross-linking for third generation(non-surface cross-linked) superabsorbent polymers; and

FIGS. 3-4 are graphical illustrations of AUL of various materials.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Thus, the present inventor has surprisingly and unexpectedly discoveredthat the use of a non-surface cross-linked superabsorbent polymer, incombination with a cellular matrix of a foamed isocyanate-based polymer,improves the AUL of the foam isocyanate-based polymer relative to theretention capacity of the latter. Specifically, the present inventor hasdiscovered that the combination of the non-surface cross-linkedsuperabsorbent polymer with the cellular matrix of a foamedisocyanate-based polymer drastically reduces and almost eliminates thedependence of AUL on the degree of cross-linking of the superabsorbentpolymer. This is a completely surprising discovery in the context of thetrends illustrated in FIGS. 1 and 2. Specifically, the effect of theseFigures is the teaching that the gap between retention capacity and AULis a maximum at low cross-link density of the superabsorbent polymer,and that this gap is narrowed only when the cross-link density of thesuperabsorbent polymer is increased. The present inventor hassurprisingly and unexpectedly discovered that the gap may besignificantly reduced and almost eliminate using a low cross-linkdensity superabsorbent polymer if such polymer is combined with a foamedisocyanate polymer. Practically, this translates into the ability to uselower cost (10% or more) superabsorbent polymers to meet a targetretention and AUL.

Preferably, the cellular matrix of the foamed isocyanate-based polymerhas a cell size of at least about 30 cells/inch when measured pursuantto ASTM D3576-77. Those of skill in art will recognize that isequivalent to a cell size of at least about 1/30 inch, at least about1.18 cells/mm or at least about 0.847 mm. Thus, while the unitcells/inch is used hereinbelow, conversion to these other units shouldbe considered supported in this specification. Preferably, the cell sizeof the cellular matrix is in the range of from about 30 to about 80,more preferably from about 30 to about 60, most preferably from about 30to about 45, cells/inch when measured pursuant to ASTM D3576-77.

In another preferred embodiment of the present foamed isocyanate-basedpolymer, the non-surface cross-linked superabsorbent polymer has aparticle size of at least about 400 μm. As used throughout thisspecification, the term "particle size" is intended to have a broadmeaning and relates to the largest dimension of the particles ofsuperabsorbent polymer. Thus, the superabsorbent polymers useful in thepresent invention include particles (substantially spherical orirregular shaped), flakes and fibers.

The present invention relates to, inter alia, a foamed isocyanate-basedpolymer comprising a non-surface cross-linked superabsorbent polymer andto a process for production thereof. Generally, the present foamedisocyanate-based polymer is selected from the group comprisingpolyurethane foam, polyurea foam, polyisocyanurate foam, urea-modifiedpolyurethane foam, urethane-modified polyurea foam, urethane-modifiedpolyisocyanurate foam and urea-modified polyisocyanurate foam. Thepreferred foamed isocyanate-based polymer is selected from the groupconsisting of polyurethane foam and urea-modified polyurethane foam. Themost preferred isocyanate-based polymer is polyurethane foam. As isknown in the art, the term "modified", when used in conjunction with apolyurethane, polyurea or polyisocyanurate means that up to 50% of thepolymer backbone forming linkages have been substituted.

Each embodiment of the present process comprises reacting and expanding(via a suitable catalyst and blowing agent) a mixture comprising anisocyanate, an active hydrogen-containing compound and a non-surfacecross-linked superabsorbent polymer. Preferably, the non-surfacecross-linked superabsorbent polymer has a particle size of 400 μm and iscapable of absorbing at least about 10 times its weight of 0.9 wt./wt. %aqueous NaCl solution maintained at a temperature in the range of fromabout 20° to about 25 ° C. The active hydrogen-containing compoundcomprises from about 10% to 100% by weight of a hydrophilic activehydrogen-containing compound and from 0 to about 90% by weight anon-hydrophilic active hydrogen-containing compound.

The isocyanate suitable for use in the substantially uniform mixture isnot particularly restricted and the choice thereof is within the purviewof a person skilled in the art. Generally, the isocyanate compoundsuitable for use may be represented by the general formula:

    Q(NCO).sub.1

wherein i is an integer of two or more and Q is an organic radicalhaving the valence of i. Q may be a substituted or unsubstitutedhydrocarbon group (e.g. an alkylene or arylene group). Moreover, Q maybe represented by the general formula:

    Q.sup.1 --Z--Q.sup.1

wherein Q¹ is an alkylene or arylene group and Z is chosen from thegroup comprising --O--, --O--Q¹ --, --CO--, --S--, --S--Q¹ --S-- and--SO₂ --. Examples of isocyanate compounds which fall within the scopeof this definition include hexamethylene diisocyanate,1,8-diisocyanato-p-methane, xylyl diisocyanate, (OCNCH₂ CH₂ CH₂ OCH₂O)₂, 1-methyl-2,4-diisocyanatocyclohexane, phenylene diisocyanates,toluene diisocyanates, chlorophenylene diisocyanates,diphenylmethane-4,4'-diisocyanate, naphthalene-1,5-diisocyanate,triphenylmethane-4,4',4'-triisocyanate andisopropylbenzene-alpha-4-diisocyanate.

In another embodiment, Q may also represent a polyurethane radicalhaving a valence of i. In this case Q(NCO)_(i) is a compound which iscommonly referred to in the art as a prepolymer. Generally, a prepolymermay be prepared by reacting a stoichiometric excess of an isocyanatecompound (as defined hereinabove) with an active hydrogen-containingcompound (as defined hereinafter), preferably thepolyhydroxyl-containing materials or polyols described below. In thisembodiment, the polyisocyanate may be, for example, used in proportionsof from about 30 percent to about 200 percent stoichiometric excess withrespect to the proportion of hydroxyl in the polyol. The prepolymer maythen be reacted with a polyol (not alwyas necessary), aqueous blowingagent (water), catalyst and, optionally, other additives, to produce apolyurethane foam or an amine to produce a polyurea-modifiedpolyurethane.

In another embodiment, the isocyanate compound suitable for use in theprocess of the present invention may be selected from diners and trimersof isocyanates and diisocyanates, and from polymeric diisocyanateshaving the general formula:

     Q(NCO).sub.i !.sub.j

wherein both i and j are integers having a value of 2 or more, and Q" isa polyfunctional organic radical, and/or, as additional components inthe reaction mixture, compounds having the general formula:

    L(NCO).sub.i

wherein i is an integer having a value of 1 or more and L is amonofunctional or polyfunctional atom or radical. Examples of isocyanatecompounds which fall with the scope of this definition includeethylphosphonic diisocyanate, phenylphosphonic diisocyanate, compoundswhich contain a=Si--NCO group, isocyanate compounds derived fromsulfonamides (QSO₂ NCO), cyanic acid and thiocyanic acid.

See also for example, British patent No. 1,453,258, the contents ofwhich are incorporated herein by reference.

Non-limiting examples of suitable isocyanates include: 1,6-hexamethylenediisocyanate, 1,4-butylene diisocyanate, furfarylidene diisocyanate,2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,4'-diphenylmethanediisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenylpropanediisocyanate, 4,4'-diphenyl-3,3'-dimethyl methane diisocyanate,1,5-naphthalene diisocyanate, 1-methyl-2,4-diisocyanate-5-chlorobenzene,2,4-diisocyanato-s-triazine, 1-methyl-2,4-diisocyanato cyclohexane,p-phenylene diisocyanate, m-phenylene diisocyanate, 1,4-naphthalenediisocyanate, dianisidine diisocyanate, bitoluene diisocyanate,1,4-xylylene diisocyanate, 1,3-xylylene diisocyanate,bis-(4-isocyanatophenyl)methane,bis-(3-methyl-4-isocyanatophenyl)methane, polymethylene polyphenylpolyisocyanates and mixtures thereof. A more preferred isocyanate isselected from the group comprising 2,4'-diphenylmethane diisocyanate,4,4'-diphenylmethane diisocyanate and mixtures thereof, for example, amixture comprising from about 15 to about 25 percent by weight2,4'-diphenylmethane diisocyanate and from about 75 to about 85 percentby weight 4,4'-diphenylmethane diisocyanate. An example of such anisocyanate is commercially available from Imperial Chemical Industriesunder the tradename Rubinate M and from The Dow Chemical Company underthe tradename PAPI 4027. The most preferred isocyanate is selected fromthe group comprising 2,4-toluene diisocyanate, 2,6-toluene diisocyanateand mixtures thereof, for example, a mixture comprising from about 75 toabout 85 percent by weight 2,4-toluene diisocyanate and from about 15 toabout 25 percent by weight 2,6-toluene diisocyanate. An example of suchan isocyanate is commercially available from The Dow Chemical Companyunder the tradename Voranate T80.

The active hydrogen-containing compound used in the uniform mixturecomprises from about 10% to 100% by weight of a hydrophilic activehydrogen-containing compound and from 0 to about 90% by weight anon-hydrophilic active hydrogen-containing compound. Preferably, theactive hydrogen-containing compound comprises from about 20% to about90%, more preferably from about 40% to about 90%, most preferably fromabout 60% to about 80%, by weight of a hydrophilic activehydrogen-containing compound and from about 10% to about 80%, morepreferably from about 10% to about 60%, most preferably from about 20%to about 30%, by weight a non-hydrophilic active hydrogen-containingcompound.

Preferably, the hydrophilic active hydrogen-containing compound is ahydrophilic polyol. As is known in the term "hydrophilic polyol" isintended to mean a polyol which confers hydrophilicity to the foamproduct. Ideally the hydrophilic polyol has a molecular weight in therange of from about 1500 to about 6000. Preferably, the hydrophilicpolyol is selected from the group consisting of diols, triols, tetrolsand mixtures thereof, each of which contain polyoxyalkylene groups, thepolyoxyalkylene groups comprising at least about 25, more preferablyfrom about 40 to about 85, most preferably from about 55 to about 85,percent by weight of ethylene oxide. As is known in the art, the balanceof the polyoxyalkylene groups is conventionally made up of one or bothof propylene oxide and butylene oxide, preferably solely propyleneoxide. A particularly preferred hydrophilic polyol is commerciallyavailable from Arco Chemical Company under the tradename Arcol 2580.Another preferred hydrophilic polyol is commercially available from TheDow Chemical Company under the tradename Voranol CP1421. Yet anotherpreferred hydrophilic polyol is commercially available from BASFCorporation under the tradename Pluracol 593.

Alternatively, if it is desired to produce a polyurea, the activehydrogen-containing compound may be derived from a hydrophilic polyol asdescribed above which as been reacted or capped with an amine. Suchamination is within the purview of a person skilled in the art.

The non-hydrophilic active hydrogen-containing compound, if present, isselected from the group consisting of non-hydrophilic polyols,polyamines, polyamides, polyimines, polyolamines and mixtures thereof.

If the process is utilized to produce a polyurethane foam, thenon-hydrophilic active hydrogen-containing compound is typically anon-hydrophilic polyol. Generally, if such non-hydrophilic polyolscontain or are based on ethylene oxide, the ethylene oxide will bepresent in amounts of less than about 20% by weight. The choice of sucha polyol is not particularly restricted and is within the purview of aperson skilled in the art. For example, the polyol may be ahydroxyl-terminated compound selected from the group comprisingpolyether, polyester, polycarbonate, polydiene and polycaprolactone. Thepolyol may be selected from the group comprising hydroxyl-terminatedpolyhydrocarbons, hydroxyl-terminated polyformals, fatty acidtriglycerides, hydroxyl-terminated polyesters, hydroxymethyl-terminatedpolyesters, hydroxymethyl-terminated perfluoromethylenes, polyalkyleneether glycols, polyalkylenearyleneether glycols and polyalkyleneethertriols. The polyol may also be selected from the group comprising adipicacid-ethylene glycol polyester, poly(butylene glycol), poly(propyleneglycol) and hydroxyl-terminated polybutadiene--see, for example, Britishpatent No. 1,482,213, the contents of which are incorporated herein byreference. Preferably, such a polyol has a molecular weight in the rangeof from about 200 to about 20,000, more preferably from about 1,500 toabout 4,300, most preferably from about 2,500 to about 3,500. Ideally,such a polyol would contain predominantly secondary hydroxyl groups.

As discussed above, it is possible to utilize a prepolymer technique toproduce a polyurethane foam within the scope of the present invention.In one embodiment, it is contemplated that the prepolymer be prepared byreacting an excess of isocyanate with a hydrophilic polyol (as discussedabove). The prepolymer could then be reacted with a non-hydrophilicpolyol (as discussed above) to produce a polyurethane foam or an amineto produce a polyurea-modified polyurethane. In another embodiment, itis contemplated that the prepolymer be prepared by reacting an excess ofisocyanate with a non-hydrophilic polyol (as discussed above). Theprepolymer could then be reacted with a hydrophilic polyol (as discussedabove) to produce a polyurethane foam. In yet another embodiment, if asingle polyol provides a desirable overall ethylene oxide content (asdiscussed above), the prepolymer can be prepared and reacted to producepolyurethane using the same polyol.

If the process is utilized to produce a polyurea-modified polyurethanefoam, the non-hydrophilic active hydrogen-containing compound comprises,at least in part, compounds wherein hydrogen is bonded to nitrogen.Preferably such compounds are selected from the group comprisingpolyamines, polyamides, polyimines and polyolamines, more preferablypolyamines. Non-limiting examples of such compounds include primary andsecondary amine terminated polyethers. Preferably such polyethers have amolecular weight of greater than about 1500, a functionality of from 2to 6, and an amine equivalent weight of from about 200 to about 6,000.Such amine terminated polyethers are typically made from an appropriateinitiator to which a lower alkylene (e.g. ethylene, propylene, butyleneand mixtures thereof) oxide is added with the resulting hydroxylterminated polyol being subsequently aminated. If two or more alkyleneoxides are used, they may be present either as random mixtures or asblocks of one or the other polyether. For ease of amination, it isespecially preferred that the hydroxyl groups of the polyol beessentially all secondary hydroxyl groups. Typically, the amination stepreplaces the majority but not all of the hydroxyl groups of the polyol.

If the process is used to produce a polyurethane foam or a urea-modifiedpolyurethane, it is possible, and indeed preferred, to use a singlepolyol or a mixture of polyols which possesses an overall ethylene oxidecontent in the range of from about 15 to about 80, preferably from about20 to about 70, more preferably from about 35 to about 70, mostpreferably from about 50 to about 65, percent by weight, the remaindercomprised of other polyoxyalkylene groups such as propylene oxide,butylene oxide or mixtures thereof. While a preferred and practicalmethod of achieving such an overall ethylene oxide content is byblending a hydrophilic polyol and a non-hydrophilic polyol as describedhereinabove, it will be appreciated that it is possible and likely evenpreferred to use a single polyol which possesses substantially the sameethylene oxide content as a mixture of a hydrophilic polyol and anon-hydrophilic polyol. Such a polyol is disclosed in copending U.S.patent application Ser. No. 08/576,695, filed Dec. 21, 1995, thecontents of which are hereby incorporated by reference.

The non-surface cross-linked superabsorbent polymer used in the presentinvention is capable of absorbing at least about 10 times its weight of0.9 wt./wt. % aqueous NaCl solution maintained at a temperature in therange of from about 20° to about 25° C. A discussion on non-surfacecross-linked superabsorbent polymers may be found in "SUPERABSORBENTPOLYMERS Science and Technology", ACS Symposium Series 573, Edited byBucholz et al. (1994), the contents of which are hereby incorporated byreference. Preferably, the non-surface cross-linked superabsorbentpolymer is a synthetic polymer such as a cellulosic polymer or a polymerof at least one of an acrylic monomer and vinyl monomer, although it ispossible to use other materials such as copolymers of maleic acid andisobutylene (typically in fiber form), cross-linked polyethylene oxideand polyethers. A non-limiting example of a suitable cellulosic polymeris a carboxymethyl cellulose and alkali metal salts thereof. Anon-limiting example of a suitable polymer of at least one of an acrylicmonomer and vinyl monomer may be selected from the group consisting ofpolyvinylpyrrolidone, sulfonated polystyrene, polysulfethyl acrylate,poly(2-hydroxyethylacrylate), polyacrylamide, poly(acrylic acid) andalkali metal salts thereof, poly(acrylic acid alkali metal salt), starchmodified polyacrylic acid and alkali metal salts thereof, poly(starchmodified acrylic acid alkali metal salt), hydrolyzed polyacrylonitrileand alkali metal salts thereof, poly(hydrolyzed polyacrylonitrile alkalimetal salt), poly(vinyl alcohol acrylic acid alkali metal salt), saltsthereof and mixtures thereof. Most preferably, the non-surfacecross-linked superabsorbent polymer is a poly(acrylic acid alkali metalsalt) such as poly(sodium acrylate).

While the amount of non-surface cross-linked superabsorbent polymer usedin the present process is not particularly restricted, it is preferredthat the non-surface cross-linked superabsorbent polymer be present inan amount up to about 150 parts by weight per hundred parts by weight ofactive hydrogen-containing compound used to produce the foamedisocyanate-based polymer. More preferably, the non-surface cross-linkedsuperabsorbent polymer is present in an amount in the range of fromabout 20 to about 80 parts, even more preferably from about 25 to about75, most preferably from about 30 to about 65, by weight per hundredparts by weight of active hydrogen-containing compound used to producethe foamed isocyanate-based polymer. Of course, as improvements are madeto non-surface cross-inked superabsorbent polymers, it is contemplatedthat the loading level required in the present foamed isocyanate-basedpolymer may be reduced while maintaining a given absorption, retentionand AUL.

As is known in the art, aqueous blowing agents such as water can be usedas a reactive blowing agent in the production of foamed isocyanate-basedpolymers. Specifically, water reacts with the isocyanate forming carbondioxide which acts as the effective blowing agent in the final foamedpolymer product. Optionally, organic blowing agents may be used inconjunction with the aqueous blowing agent, although the use of suchblowing agents is generally being curtailed for environmentalconsiderations. It is known in the art that the amount of water used asa blowing agent in the preparation of a foamed isocyanate-based polymeris conventionally in the range of from about 0.5 to as high as about 20or more parts by weight, preferably from about 1.0 to about 5.0 parts byweight, based on 100 parts by weight of the total activehydrogen-containing compound content in the reaction mixture. Since theamount of water used in the production of a foamed isocyanate-basedpolymer is limited by the fixed properties expected in the foamedpolymer, it may be necessary, in certain circumstances, to utilize asubstantially inert liquid extenders when high loadings of fillermaterial are contemplated. Non-limiting examples of suitable liquidextenders include halogenated hydrocarbons and high molecular weighthydrocarbons.

The catalyst added to the uniform mixture of isocyanate, activehydrogen-containing compound and superabsorbent polymer is a compoundcapable of catalyzing the polymerization reaction. Such catalysts areknown, and the choice and concentration thereof is within the purview ofa person skilled in the art. See for example U.S. Pat. Nos. 4,296,213and 4,518,778, the contents of each of which is incorporated herein byreference. Non-limiting examples of suitable catalysts include tertiaryamines and/or organometallic compounds. Additionally, as is known in theart, when the objective is to produce an isocyanurate, a Lewis acid mustbe used as the catalyst, either alone or in conjunction with othercatalysts. Of course it will be understood by those skilled in the artthat a combination of two or more catalysts may be suitably used.

In one embodiment of the present process, an initial step comprises theformation of a uniform mixture comprising the isocyanate, the activehydrogen-containing compound and the non-surface cross-linkedsuperabsorbent polymer. The manner by which the uniform mixture isprepared is not particularly restricted. Thus, it is possible topreblend the components in a separate tank which is then connected to asuitable mixing device for mixing with the aqueous blowing agent andcatalyst. The aqueous blowing agent and catalyst may be fed to themixing device independently or as a mixture.

In another embodiment of the present process, an initial step comprisesthe formation of a uniform mixture comprising the aqueous blowing agent,the active hydrogen-containing compound, the catalyst and thenon-surface cross-linked superabsorbent polymer. The manner by which theuniform mixture is prepared is not particularly restricted. Thus, it ispossible to preblend the components in a separate tank which is thenconnected to a suitable mixing device for mixing with the isocyanate.The isocyanate may be fed to the mixing device in a conventional manner.

In yet another embodiment of the present process, an initial stepcomprises the provision of a preblend of the non-surfaced cross-linkedsuperabsorbent polymer with the active hydrogen-containing compound.This preblend could then be fed to a suitable mixhead which would alsoreceive independent streams of the isocyanate, the aqueous blowing agentand the catalyst. Alternatively, the aqueous blowing agent and catalyststreams could be combined prior to the mixhead, if desired. In thisembodiment, care would have to be taken to design the mixhead to ensurethat the preblend and isocyanate streams are adequately mixed at thetime that the aqueous blowing agent and catalyst stream(s) are added.

As will be clearly understood by those of skill in the art, it iscontemplated that conventional additives in the isocyanate-based polymerart be used in the process. Non-limiting examples of such additivesinclude: surfactants (e.g. organo-silicone compounds available under thetradename L-5770 from OSi), cell openers (e.g. silicone oils), extenders(e.g. halogenated paraffins commercially available as Cereclor S45 fromICI plc), cross-linkers (e.g. low molecular weight reactivehydrogen-containing compositions), pigments/dyes, flame retardants (e.g.halogenated organo-phosphoric acid compounds), inhibitors (e.g. weakacids), nucleating agents (e.g. diazo compounds), anti-oxidants,plasticizers/stabilizers (e.g. sulphonated aromatic compounds) andbiocides. The amounts of these additives conventionally used would bewithin the purview of a person skilled in the art.

A particularly preferred class of additives which may be used herein isthat of fillers. The particular advantage is that various fillers suchas pulp and ground post-consumer goods (e.g. tire, reaction injectionmolded parts, reinforced reaction injection mold parts,off-specification personal hygiene devices, etc.) is that they can beeffectively recycled in the present foamed isocyanate-based polymer withlittle or no compromise of absorption, retention and AUL properties.

Once the aqueous blowing agent, catalyst, isocyanate, activehydrogen-containing compound and non-surface cross-linked superabsorbentpolymer pursuant to the present process are combined, a reaction mixtureis formed. This reaction mixture is then expanded to produce the presentfoamed isocyanate-based polymer. As will be apparent to those of skillin the art, the process of the present invention is useful in theproduction of slab foam, molded articles and the like. Thus, as will beapparent to a person skilled in the art, the manner by which expansionof the reaction mixture is effected will be dictated by the type of foambeing produced. The present process may be conducted using aconventional low pressure mechanical mixhead (typically used to produceslab foam) or a conventional high pressure impingement mixhead(typically used to produce molded foam).

The product of the present process is a foamed isocyanate-based polymerhaving a cellular structure and containing a superabsorbent material,the polymer being capable of: (i) absorbing at least about 10 times itsweight of a 0.9% wt./wt. % aqueous NaCl solution maintained at atemperature of from about 200 to about 25° C., and (ii) retaining atleast about 10 times its weight of absorbed NaCl solution which is boundto the superabsorbent material. Preferably the polymer is capable of:(i) absorbing at from about 10 to about 50, more preferably from about10 to about 30, most preferably from about 10 to about 20, times itsweight of a 0.9 wt./wt. % aqueous NaCl solution maintained at atemperature of from about 20° to about 25° C., and (ii) retaining fromabout 10 to about 50, more preferably from about 10 to about 30, mostpreferably from about 10 to about 20, times its weight of absorbed 0.9wt./wt. % aqueous NaCl solution which is bound to the superabsorbentmaterial.

The ability of the foamed isocyanate-based polymer to absorb 0.9 wt./wt.% aqueous NaCl solution (also referred to as "the saline solution") canbe assessed by following "tea bag" protocol: (i) weigh empty tea bag(W₁); (ii) weigh test sample of foamed isocyanate-based polymer(W₂)--the preferred test sample is a disk having a diameter of 2 inchesand a thickness of 1/2 inch, (iii) place test sample inside empty teabag and seal tea bag, (iv) completely submerge sealed tea bag in thesaline solution maintained at a temperature of 22°±2° C. for a period of1 hour, (v) remove sealed tea bag from saline solution and suspend toallow gravity drainage device for 5 minutes, (vi) weigh sealed tea bag(W₃), and (vii) calculate (W₃ -W₁ -W₂)/W₂ and report as the amount of0.9 wt./wt. % aqueous NaCl solution absorbed as a multiple of the weightof the original test sample of foamed isocyanate-based polymer (W₂)(another way in which to report the results is as units mass of 0.9wt./wt. % aqueous NaCl solution absorbed per unit mass of foam). Theability of the foamed isocyanate-based polymer to retain aqueous liquidcan be assessed by conducting the absorption protocol and the followingsubsequent steps: (viii) place the sealed tea bag on a retention (drip)screen and compress the sealed tea bag containing absorbed salinesolution with a compressive force of at least about 1.0 psi (morepreferably at about 1.03 psi) for a period of 1 minute, (ix) weigh testsample (W₄), and (x) calculate (W₄ -W₁ -W₂)W₂ and report as the amountof 0.9 wt./wt. % aqueous NaCl solution retained as a multiple of theweight of the original test sample of foamed isocyanate-based polymer(W₂) (another way in which to report the results is as units mass of 0.9wt./wt. % aqueous NaCl solution retained per unit mass of foam). Thus,the two properties distinguish between saline which is physically andchemically bound to the foam (i.e. absorbed) and saline solution whichonly chemically bound to the foam (i.e. retained). For furtherinformation, see Chapter 8 (and the references cited therein) of"SUPERABSORBENT POLYMERS Science and Technology", ACS Symposium Series573, Edited by Bucholz et al. (1994), the contents of which are herebyincorporated by reference.

As discussed hereinabove another property of the present foamedisocyanate-based polymer which is useful for assessing its ability toabsorb fluids is known as Absorbency Under Load or AUL. This property isdiscussed in more detail in U.S. Pat. No. 5,147,343, the contents ofwhich are hereby incorporated by reference. As is known, AUL is believedto be a function of one or more of the following factors: (1) gelstiffness while swelling, (2) ability to imbibe the fluid by osmotic andinternal electrostatic repulsion forces, (3) surface wettability of thefoamed polymer, and (4) particle size distribution when wetted.

In the context of the present invention, it is preferred to use thefollowing protocol for determine the AUL of the foamed isocyanate-basedpolymer: (i) weigh an AUL device (W₁)--the AUL device is a 2 inch I.D.acrylic tube having a closed, perforated end and a series of 2 inchdiameter weights which are used in sufficient number to provide apredetermined applied force (e.g. 0.3 psi, 0.5 psi, 0.9 psi); (ii) weightest sample of foamed isocyanate-based polymer (W₂)--the test sample isa disk having a diameter of 2 inches and a thickness of 1/2 inch, (iii)remove the weight(s) from the AUL device, place the test sample insidethe acrylic tube of the AUL device such that the test sample is flushwith the closed, perforated end of the acrylic tub, and place theweight(s) on top of the test sample, (iv) place the AUL device in a pancontaining 0.9 wt./wt. % aqueous NaCl solution maintained at atemperature of 22°±2° C. for a period of 1 hour--the pan as designedshould have bottom ridges or other means sufficient to allow freemovement of fluid under AUL device when the latter is placed in the pan,(v) remove AUL device from pan and allow to drain for 1 minute, (vi)wipe off excess fluid from exterior of AUL device and weigh AUL device(W₃), and (vii) calculate (W₃ -W₁ -W₂)/W₂ and report as the amount of0.9 wt./wt. % aqueous NaCl solution absorbed as the AUL, at thepredetermined load, of the original test sample of foamedisocyanate-based polymer (W₂).

The present foamed isocyanate-based polymer has an AUL, at 0.5 psi, ofat least about 7, preferably in the range of from about 7 to about 50,more preferably from about 7 to about 40, most preferably from about 7to about 30, grams of 0.9 wt./wt. % aqueous NaCl solution absorbed pergram of foamed isocyanate-based polymer. Further, the present foamedisocyanate-based polymer has an AUL, at 0.9 psi, of at least about 7,preferably in the range of from about 7 to about 40, more preferablyfrom about 7 to about 30, most preferably from about 7 to about 20,grams of 0.9 wt./wt. % aqueous NaCl solution absorbed per gram of foamedisocyanate-based polymer.

Thus, the retention and AUL properties of the present foamedisocyanate-based polymer are generally predictive of the retention andAUL properties which are desirable in a principal practical applicationof the present invention. Specifically, if the present foam product isused in the core of a diaper, the aqueous fluid retention propertiesreferred to above are advantageous since they are predictive of a diapercore which will absorb, inter alia, urine while mitigating againstsignificant amounts of absorbed urine being squeezed out of the coreagainst the skin of the child or leaking out of the diaper.

The type of non-surface cross-linked superabsorbent polymer and theamount thereof present in the foamed isocyanate-based polymer is asdiscussed hereinabove in regard to the present process.

The present foamed isocyanate-based polymer has multitude of potentialapplication. For example, the present foamed isocyanate-based polymerwill is useful as the core of a personal hygiene device. However, thepresent foamed isocyanate-based polymer will find use in manyapplications in which fluid management or control is desirable, such asany of the following non-limiting examples: water bed core, gasolinetanks, flood control, insect control, desiccants, horticulturalapplications, oil spill clean-up and the like.

Thus, as will be appreciated by those of skill in the art, the foamproduct of the present invention having advantageous aqueous fluid (e.g.saline) absorption, retention and AUL properties, is the direct productof polymerization and expansion. In other words, the advantageousproperties of the foam product of the present invention are notdependent on any specific, complicated and expensive reticulation (orother post-treatment) step such as taught by U.S. Pat. No. 4,985,467Kelly et al.!, the contents of which are hereby incorporated byreference. Those of skill in the art will recognize that the foamproduct of the present invention is not a thermally reticulatedproduct--i.e. the foam product of the present invention isnon-reticulated. Rather, the foam product of the present invention is acellular material having an open cell structure (i.e. cells with crackedor broken membranes between cell struts as discussed above) as opposedto a skeletal matrix or structure as taught by Kelly et al.

The present foamed isocyanate-based polymer preferably has a density offrom about 1.0 pcf (about 16.0 kg/m³) to about 15.0 pcf (about 240kg/m³), more preferably from about 1.0 pcf (about 16.0 kg/m³) to. about12.0 pcf (about 192 kg/m³), even more preferably from about 1.0 pcf(about 16.0 kg/m³) to about 8.0 pcf (about 128 kg/m³), most preferablyfrom about 1.5 pcf (about 16.0 kg/m³) to about 5.0 pcf (about 80.1kg/m³).

Embodiments of the present invention will now be described withreference to the following Examples which should not be construed aslimiting the scope of the invention. The term "pbw" used in the Examplesrefers to parts by weight.

In the Examples the following compounds were used:

1. DABCO-T16, a polymerization catalyst commercially available from AirProducts and Chemicals, Inc.;

2. L5770, an organo-silicone surfactant available under the tradenameL-5770 from OSi;

3. C255, an amine catalyst available from OSi;

4. Arcol 2580, a hydrophilic polyether polyol having a molecular weightof approximately 5,000 and an ethylene oxide content of approximately75% by weight, available from Arco Corporation;

5. Voranol 3010, a non-hydrophilic polyether polyol having a molecularweight of approximately 3000 and an ethylene oxide content of less thanabout 20% by weight, commercially available from The Dow ChemicalCompany;

6. TDI 80, a blend of 80% by weight 2,4-toluene diisocyanate, and 20% byweight 2,6-toluene diisocyanate commercially available from BayerCorporation under the tradename Mondur TD-80 Grade A;

7. Sanwet IM3000, a non-surface cross-linked starch grafted sodiumpolyacrylate available from Hoechst Celanese Corporation;

8. Sanwet IM4500, a surface cross-linked starch grafted sodiumpolyacrylate available from Hoechst Celanese Corporation;

9. SXM-70, a surface cross-linked poly(sodium acrylate) available fromStockhausen Inc.; and

10. SAB 800, a non-surface cross-linked polyacrylate/polyalcoholcopolymer available from Stockhausen Inc.

EXAMPLES1-4

In these Examples, a series of foam samples were made with various ofthe superabsorbent polymers listed above. The general formulation usedin these Examples may be found in Table 1.

                  TABLE 1                                                         ______________________________________                                        Ingredient       Amount (parts)                                               ______________________________________                                        Arcol 2580       70                                                           Voranol 3010     30                                                           L5770            1.2                                                          C255             1.0                                                          Water            2.8                                                          Superabsorbent polymer                                                                         50                                                           DABCO-T16        0.1                                                          TDI 80           Sufficient amount to                                                          provide an isocyanate                                                         index of about 1.05.                                         ______________________________________                                    

The foam samples were produced according to the following procedure. Thepolyols were mixed with the L5770, the C255 and water. Thesuperabsorbent polymer was added to and blended with the mixture. TheDABCO-T16 was added with continued mixing. Thereafter, the TDI 80 wasadded with mixing and the resulting reaction mixture was poured into anopen container and allowed to expand to result in a polyurethane foam.

The foam was cut into appropriate sample size (described above) andsubjected to saline (0.9 wt./wt. % aqueous NaCl solution) absorption,retention and AUL (0.5 psi and 0.9 psi) testing as describedhereinabove.

A first set of absorption, retention, AUL @0.5 psi and AUL @0.9 psiproperties of the foam are reported in Tables 2, 3, 4 and 5,respectively. In Tables 2-5, absorption, retention, AUL @0.5 and AUL@0.9 are reported as the weight of 0.9 wt./wt. % aqueous NaCl solutionabsorbed, retained or absorbed under load, as appropriate, perequivalent weight of superabsorbent polymer and were calculatedaccording to the formula: ##EQU1## wherein y is 3 for absorption and AULand y is 4 for retention, and W₁ and W₂ are as defined hereinabove inthe protocols for absorption, retention and AUL. Those of skill in theart will recognize that the factor 0.271 derives from the amount of SAP,on a weight percent basis, adjusted via a conventional calculation forgas loss of material, of the formulation reported in Table 1.

Also reported for each Example in Tables 2-5, for comparative purposes,are the absorption, retention and AUL properties for the superabsorbentpolymer (i.e. as is, not in a foam) and for a 50/50 weight percentmixture of the superabsorbent polymer and pulp (Note: pulp used alonehad an AUL of 10.90 g saline absorbed under load per gram of pulp). Forabsorption, retention and AUL, each result reported in Tables 2-5 is anaverage of four samples.

                  TABLE 2                                                         ______________________________________                                        Absorption                                                                           SAP.sup.1 /Example                                                     Product Test                                                                           IM3000/1  IM4500/2  SAB800/3                                                                              SXM70/4                                  ______________________________________                                        SAP.sup.1 alone                                                                        51.66     44.62     40.57   41.64                                    SAP.sup.1 /pulp                                                                        74.54     76.34     68.54   73.77                                    SAP.sup.1 /foam                                                                        62.93     59.71     64.65   54.15                                    ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Retention                                                                            SAP.sup.1 /Example                                                     Product Test                                                                           IM3000/1  IM4500/2  SAB800/3                                                                              SXM70/4                                  ______________________________________                                        SAP.sup.1 alone                                                                        45.27     40.82     39.40   36.00                                    SAP.sup.1 /pulp                                                                        48.96     56.46     48.46   51.51                                    SAP.sup.1 /foam                                                                        49.10     43.66     44.46   47.89                                    ______________________________________                                         .sup.1 Superabsorbent polymer.                                           

                  TABLE 4                                                         ______________________________________                                        AUL @ 0.5 psi                                                                        SAP.sup.1 /Example                                                     Product Test                                                                           IM3000/1  IM4500/2  SAB800/3                                                                              SXM70/4                                  ______________________________________                                        SAP.sup.1 alone                                                                        12.29     25.69     17.08   23.28                                    SAP.sup.1 /pulp                                                                        22.00     30.79     21.36   22.38                                    SAP.sup.1 /foam                                                                        34.43     35.70     33.21   35.11                                    ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        AUL @ 0.9 psi                                                                        SAP.sup.1 /Example                                                     Product Test                                                                           IM3000/1  IM4500/2  SAB800/3                                                                              SXM70/4                                  ______________________________________                                        SAP.sup.1 alone                                                                        11.90     18.02     12.82   17.13                                    SAP.sup.1 /pulp                                                                        15.32     24.34     19.12   24.33                                    SAP.sup.1 /foam                                                                        29.77     28.82     29.69   29.13                                    ______________________________________                                         .sup.1 Superabsorbent polymer.                                           

A second set of absorption, retention, AUL @0.5 psi and AUL @0.9 psiproperties of the foam are reported in Tables 6, 7, 8 and 9,respectively. In Tables 6-9, absorption, retention, AUL @0.5 and AUL@0.9 are reported as the weight of 0.9 wt./wt. % aqueous NaCl solutionabsorbed, retained or absorbed under load, as appropriate, perequivalent weight of foam (i.e. using to original test protocolsdescribed prior to the Examples).

As will be understood by those of skill in the art Examples 2 and 4involved the use of a surface cross-linked superabsorbent polymer(IM4500 and SXM70, respectively) and are provided for comparativepurposes only.

The results reported in Table 2-5 clearly demonstrate that the AUL ofthe non-surface cross-linked superabsorbent polymer changessignificantly depending on its environment. Specifically, the AUL of thenon-surface cross-linked superabsorbent polymer alone and dispersed inpulp, was significantly lower when compared to that for surfacecross-linked superabsorbent polymer alone and dispersed in pulp,respectively. In contrast, when the non-surface cross-linkedsuperabsorbent polymer was dispersed in a polyurethane foam as describedabove, the AUL thereof improved to substantially the same or greaterthan that of the surface cross-linked superabsorbent polymer. This canalso be appreciated in the context of FIGS. 3 and 4 which illustrate howthe non-surface cross-linked superabsorbent polymers (IM3000 and SAB800)improve in AUL when they are dispersed in foam to a level substantiallythe same as or greater than that obtained using surface cross-linkedsuperabsorbent polymers (IM4500 and SXM70).

                  TABLE 6                                                         ______________________________________                                        Absorption                                                                           SAP.sup.1 /Example                                                     Product Test                                                                           IM3000/1  IM4500/2  SAB800/3                                                                              SXM70/4                                  ______________________________________                                        SAP.sup.1 alone                                                                        51.36     44.62     40.57   41.64                                    SAP.sup.1 /pulp                                                                        37.27     38.17     36.88   34.27                                    SAP.sup.1 /foam                                                                        17.21     17.57     18.53   15.73                                    ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Retention                                                                            SAP.sup.1 /Example                                                     Product Test                                                                           IM3000/1  IM4500/2  SAB800/3                                                                              SXM70/4                                  ______________________________________                                        SAP.sup.1 alone                                                                        45.27     40.82     39.40   36.00                                    SAP.sup.1 /pulp                                                                        24.48     28.24     24.23   25.76                                    SAP.sup.1 /foam                                                                        13.82     13.22     13.05   14.03                                    ______________________________________                                         .sup.1 Superabsorbent polymer.                                           

                  TABLE 8                                                         ______________________________________                                        AUL @ 0.5 psi                                                                        SAP.sup.1 /Example                                                     Product Test                                                                           IM3000/1  IM4500/2  SAB800/3                                                                              SXM70/4                                  ______________________________________                                        SAP.sup.1 alone                                                                        12.29     25.69     17.08   23.28                                    SAP.sup.1 /pulp                                                                        15.46     24.47     14.93   18.08                                    SAP.sup.1 /foam                                                                        8.38      9.67      9.00    8.65                                     ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        AUL @ 0.9 psi                                                                        SAP.sup.1 /Example                                                     Product Test                                                                           IM3000/1  IM4500/2  SAB800/3                                                                              SXM70/4                                  ______________________________________                                        SAP.sup.1 alone                                                                        45.27     40.82     39.40   36.00                                    SAP.sup.1 /pulp                                                                        24.48     28.24     24.23   25.76                                    SAP.sup.1 /foam                                                                        13.82     13.22     13.05   14.03                                    ______________________________________                                         .sup.1 Superabsorbent polymer.                                           

EXAMPLES 5-9

In these Examples, a series of foam samples were made with various ofthe superabsorbent polymers listed above at various loading levels. Thegeneral formulation used in these Examples may be found in Table 10.

                  TABLE 10                                                        ______________________________________                                        Ingredient      Amount (parts)                                                ______________________________________                                        Arco 2580       70                                                            Voranol 3010    30                                                            L5770           1.2                                                           C255            1.0                                                           Water           2.8                                                           Superabsorbent polymer                                                                        variable                                                      DABCO-T16       0.1                                                           TDI 80          Sufficient amount to                                                          provide an isocyanate                                                         index of about 1.05.                                          ______________________________________                                    

The foam samples were produced according to procedure outlinedhereinabove in Examples 1-4.

The resulting foam was cut into appropriate sample size (describedabove) and subjected to saline (0.9 wt./wt. % aqueous NaCl solution)absorption, retention and AUL (0.5 psi and 0.9 psi) testing theprotocols described above. The absorption and retention properties ofthe foam are reported in Tables 11 and 12, respectively. The AULproperties of the foam at 0.5 psi and 0.9 psi are reported in Tables 13and 14, respectively. In Tables 7 and 8, AUL is reported as the weightof 0.9 wt./wt. % aqueous NaCl solution absorbed (under load) perequivalent weight of foam (cf. Examples 14). For absorption, retentionand AUL, each result reported in Tables 11-14 is an average of foursamples.

The results in Tables 11-14 demonstrate that, in virtually all cases,the absorption, retention and AUL properties of foam made withnon-surface cross-linked superabsorbent polymer were almost equal toand, in some cases, exceeded the same properties of a comparative foammade with a surface cross-linked superabsorbent polymer. Thus, it ispossible to utilize a less expensive non-surface cross-linkedsuperabsorbent polymer to produce a foam which performs virtually aswell as or even better than a foam made with more expensive surfacecross-linked superabsorbent polymer.

                  TABLE 11                                                        ______________________________________                                        Absorbance                                                                                  SAP.sup.1                                                       Example                                                                              SAP.sup.1 Loading Level                                                                    IM3000  IM4500                                                                              SAB800 SXM70                                ______________________________________                                        5      10           16.62   14.84 11.84  14.12                                6      20           18.63   16.25 11.36  12.78                                7      30           19.18   17.56 13.81  14.84                                8      40           17.37   16.74 15.42  14.85                                9      50           17.21   17.57 18.53  15.73                                ______________________________________                                    

                  TABLE 12                                                        ______________________________________                                        Retention                                                                                   SAP.sup.1                                                       Example                                                                              SAP.sup.1 Loading Level                                                                    IM3000  IM4500                                                                              SAB800 SXM70                                ______________________________________                                        5      10           13.95   12.10 10.00  10.21                                6      20           13.37   12.40 10.40  11.39                                7      30           15.14   14.35 10.36  12.15                                8      40           13.60   14.30 12.01  12.07                                9      50           13.82   13.22 13.05  14.03                                ______________________________________                                         .sup.1 Superabsorbent polymer.                                           

                  TABLE 13                                                        ______________________________________                                        AUL @ 0.5 psi                                                                               SAP.sup.1                                                       Example                                                                              SAP.sup.1 Loading Level                                                                    IM3000  IM4500                                                                              SAB800 SXM70                                ______________________________________                                        5      10           7.38    6.13  5.43   7.19                                 6      20           7.78    7.11  6.88   7.57                                 7      30           7.82    8.22  8.78   7.83                                 8      40           8.89    8.61  8.58   8.40                                 9      50           8.38    9.67  9.00   8.65                                 ______________________________________                                    

                  TABLE 14                                                        ______________________________________                                        AUL @ 0.9 psi                                                                               SAP.sup.1                                                       Example                                                                              SAP.sup.1 Loading Level                                                                    IM3000  IM4500                                                                              SAB800 SXM70                                ______________________________________                                        5      10           5.92    5.22  5.44   7.38                                 6      20           6.39    6.14  6.14   7.53                                 7      30           6.75    7.23  6.68   7.75                                 8      40           7.94    7.72  7.11   8.11                                 9      50           7.41    7.81  8.05   8.29                                 ______________________________________                                         .sup.1 Superabsorbent polymer.                                           

What is claimed is:
 1. A foamed isocyanate-based polymer having acellular structure and comprising a non-surface cross-linkedsuperabsorbent polymer, the foamed isocyanate-based polymer beingcapable of: (i) absorbing at least about 10 times its weight of a 0.9wt./wt. % aqueous NaCl solution maintained at a temperature of fromabout 20° to about 25° C., and (ii) retaining at least about 10 timesits weight of absorbed aqueous NaCl solution which is bound to thesuperabsorbent polymer.
 2. The foamed isocyanate-based polymer definedin claim 1, wherein the polymer is capable of: (i) absorbing from about10 to about 50 times its weight of a 0.9 wt./wt. % aqueous NaCl solutionmaintained at a temperature of from about 20° to about 25° C., and (ii)retaining from about 10 to about 50 times its weight of absorbed aqueousNaCl solution which is bound to the superabsorbent polymer.
 3. Thefoamed isocyanate-based polymer defined in claim 1, wherein the foamedpolymer is capable of: (i) absorbing from about 10 to about 30 times itsweight of a 0.9 wt./wt. % aqueous NaCl solution maintained at atemperature of from about 20° to about 25° C., and (ii) retaining fromabout 10 to about 30 times its weight of absorbed aqueous NaCl solutionwhich is bound to the superabsorbent polymer.
 4. The foamedisocyanate-based polymer defined in claim 1, wherein the foamed polymeris capable of: (i) absorbing from about 10 to about 20 times its weightof a 0.9 wt./wt. % aqueous NaCl solution maintained at a temperature offrom about 20° to about 25° C., and (ii) retaining from about 10 toabout 20 times its weight of absorbed aqueous NaCl solution which isbound to the superabsorbent polymer.
 5. The foamed isocyanate-basedpolymer defined in claim 1, wherein the superabsorbent polymer is asynthetic polymer.
 6. The foamed isocyanate-based polymer defined inclaim 1, wherein the superabsorbent polymer is a cellulosic polymer. 7.The foamed isocyanate-based polymer defined in claim 6, wherein thecellulosic polymer is a carboxymethyl cellulose.
 8. The foamedisocyanate-based polymer defined in claim 1, wherein the superabsorbentpolymer is a polymer of at least one of an acrylic monomer and vinylmonomer.
 9. The foamed isocyanate-based polymer defined in claim 1,wherein the superabsorbent polymer is selected from the group consistingof polyvinylpyrrolidone, sulfonated polystyrene, polysulfethyl acrylate,poly(2-hydroxyethylacrylate), polyacrylamide, polyacrylic acid,poly(acrylic acid alkali metal salt), starch modified polyacrylic acid,poly(starch modified acrylic acid alkali metal salt), hydrolyzedpolyacrylonitrile, poly(hydrolyzed polyacrylonitrile alkali metal salt)and mixtures thereof.
 10. The foamed isocyanate-based polymer defined inclaim 1, wherein the superabsorbent polymer is present in an amount upto about 150 parts by weight per hundred parts by weight of activehydrogen-containing compound used to produce the foamed isocyanate-basedpolymer.
 11. The foamed isocyanate-based polymer defined in claim 1,wherein the superabsorbent polymer is present in the range of from about20 to about 80 parts by weight per hundred parts by weight of activehydrogen-containing compound used to produce the foamed isocyanate-basedpolymer.
 12. The foamed isocyanate-based polymer defined in claim 1,wherein the superabsorbent polymer is present in the range of from about25 to about 75 parts by weight per hundred parts by weight of activehydrogen-containing compound used to produce the foamed isocyanate-basedpolymer.
 13. The foamed isocyanate-based polymer defined in claim 1,wherein the superabsorbent polymer is present in the range of from about30 to about 65 parts by weight per hundred parts by weight of activehydrogen-containing compound used to produce the foamed isocyanate-basedpolymer.
 14. A foamed polyurethane polymer comprising a non-surfacecross-linked poly(acrylic acid alkali metal salt) in an amount in therange of from about 10 to about 65 parts by weight per hundred parts byweight of polyol used to produce the foamed polyurethane polymer, thepolymer being capable of: (i) absorbing from about 10 to about 20 timesits weight of a 0.9 wt./wt. % aqueous NaCl solution maintained at atemperature of from about 20° to about 25° C., and (ii) retaining fromabout 10 to about 20 times its weight of absorbed aqueous NaCl solutionwhich is bound to the poly(acrylic acid alkali metal salt).
 15. Apersonal hygiene device having a bodily fluid absorbent layer consistingessentially of the foamed isocyanate-based polymer defined in claim 1.16. A personal hygiene device having a bodily fluid absorbent layerconsisting essentially of the foamed polyurethane polymer defined inclaim 14.